1. Field of the Invention
The present invention relates to a wound dressing, and more particularly to a wound dressing having a construction with improved skin adherence and absorptive capabilities, and methods for producing the same.
2. Discussion of Related Art
Historically, many diverse materials of various origins have been used to treat wounds by absorbing wound fluids and tissue, hereinafter generally referred to as exudate, from a wound site with some type of absorbent material. In recent years, use of polymeric-based wound care products have become increasingly popular to control wound site environmental factors such as water vapor, oxygen permeability, bacterial impermeability, and absorption of exudate. Such wound care products are tailored to meet specific requirements including conformability to a body portion, selective adherence to a wound bed, and adhesiveness to the skin surrounding the wound site.
Recently, occlusive or moisture-retentive dressings have gained increasing acceptance in treating wounds, in particular pressure sores and ulcers. A wide variety of types of structures are known in the art for use in or as occlusive dressings and generally comprise components for receiving, absorbing and retaining exudate. Typically, these wound care products include polymeric foams, polymeric films, particulate and fibrous polymers, hydrogels and hydrocolloids. Dressings with at least one of these components promote wound healing by providing a moist environment, while removing excess exudate and toxic components, and further serve as a barrier to protect the wound from secondary bacterial infection. While these known occlusive wound dressings can effectively manage a wound, many have been found to possess certain limitations or disadvantages.
In wound care, one of the main objectives of a wound dressing is to increase, improve or maximize utilization of the absorbent capacity of the dressing so as reduce or eliminate maceration, and facilitate the healing process of the wound. The control of exudate is of prime importance if a moist wound microenvironment is to be maintained. Unfortunately, many wound dressings have been found to remove all the exudate that a wound produces, thereby causing a “dry” wound that is undesirable in the wound healing process or in the alternative, such wound dressings have been found to absorb or control the exudate insufficiently, thereby leading to a pooling of the exudate which may increase the risk of bacterial proliferation and lead to infection.
Many wound dressings in the prior art include an absorbent layer having absorptive capabilities. Typically, the absorbent layer contains hydrophilic materials that absorb exudate and permit the wound dressing to be left in place for a period of days. Such absorbent layers may comprise a non-woven material or foam containing hydrocolloid particles such as the dressings described in U.S. Pat. Nos. 4,373,519 and 6,566,576, or a hydrophilic foam layer, such as in the dressings described in U.S. Pat. Nos. 5,409,472, 5,782,787, 6,040,492, 6,051,747, and 6,486,378.
While absorbent layer dressings are configured to absorb wound exudate, they often possess the disadvantage of being limited in the amount of exudate that may be absorbed. The limit to the maximum absorption of absorbent foam is often directly related to their geometrical size prior to absorbing a fluid. For example, hydrophilic foams may expand only to 12–15% of their original size. Another disadvantage is that it has been found that a certain amount of the exudate can be “squeezed” out of absorbent foam dressings due to poor liquid retention. The ability of exudates to be squeezed from the foam layer, and thus dressing itself, poses a risk of infection and may interfere with the healing of the wound.
Yet another disadvantage with known dressings is that absorption of exudate by an absorptive layer in contact with the wound causes the central portion of the applied dressing to swell and push up against the wound. Continued swelling can induce separation of the skin adherent layer from the skin outside the wound area, especially at the border of the wound dressing whereat a “curling” effect may occur. This excessive swelling of the wound dressing may further lead to leakage of the exudate from the periphery of the dressing, thereby providing a tract for the invasion of pathogenic microorganisms and further promoting maceration of the wound site.
Conventionally, a backing layer is provided that comprises a liquid impervious film that is attached to the absorbent layer to prevent exudate from seeping from the dressing. A difficulty arises during fluid uptake in that as the absorbent core expands, the backing layer must accommodate the expansion of the absorbent layer without causing curling of the dressing. An attempted solution to this problem is described in U.S. Pat. No. 4,738,257 which discloses a backing layer formed of a thin elastic sheet which is yieldable as the absorbent core swells. It has been found, however, that a liquid impervious plastic film cannot be made to sufficiently stretch in keeping with the expansion of the absorbent layer, and as a result, the film counteracting with the swelling absorbent layer may produce the aforesaid curling at the border of the dressing. Another proposed solution is provided in U.S. Pat. No. 6,040,492 which discloses a wound dressing that includes a backing layer that is attached to an absorbent foam core and includes a plurality of wrinkles that substantially flatten as the foam core swells. While the backing layer may accommodate the expansion of the foam core, the fluid uptake of this wound dressing is limited by the expandability of the foam core itself. Accordingly, due to the limited absorptive capacity of the foam core, the dressing must be replaced often.
Ideally, a wound dressing must be adhesive in nature such that it may attach to the wound site while being non-toxic and eliciting no more than a minimal allergenic response. Moreover, a wound dressing should possess the ability to prevent bacteria from entering the wound from the ambient environment while providing a suitable moisture transmission rate.
It has been found, however, that many known occlusive dressings possess the disadvantage of relying solely on a pressure sensitive adhesive layer that is used to secure the dressing to skin, for instance an acrylate glue having a high specific adhesiveness. Typically, a wound dressing with only an adhesive has a tendency to strip the central portion of the dressing from the wound when removed from the wound and thus may damage healing tissue.
Wound dressing have been commercially available that include an absorbent foam core with a wound contacting surface coated with a layer of silicone gel. The silicone gel randomly lines portions of the walls of the pores of the absorbent foam to form a plurality of randomly formed apertures. These apertures are formed by capillary action when an uncured silicone gel is applied to the foam core. One drawback to this approach is that the silicone gel may close some of the pores, and another drawback is that the holes are randomly formed which may lead to localized areas that inhibit the uptake of the exudate into the foam core. While in some applications it may be desirable to provide the wound dressing with a greater concentration of apertures at selected regions of the wound dressing to increase exudate uptake at such areas, this approach does not accommodate such a formation of a predetermined pattern of apertures. Furthermore, another drawback to this approach is that the surface roughness of the silicone layer is largely dependent upon the surface of the foam to be coated, and in the event it is desired to obtain a smooth silicone layer to be worn on the skin, this approach fails to yield such a smooth silicone layer.
Developments in the field of silicone manufacturing have led Ossur hf of Reykjavik, Iceland, and assignee of the present invention, to produce silicone products adapted for skin contact that provide superb softness, gentle skin contact, and may include unique skin care ingredients. In particular, such silicone manufacturing has led to advances in improved comfort and cushioning of prosthetic suspension liners that have excellent durability and intimacy using proprietary silicone technology of Ossur hf. It has been found that by applying the silicone technology of Ossur hf to produce an ultra-thin, perforated tacky silicone sheet, a silicone adhesive layer can be produced that possesses superior gentle adherence to wound sites while not damaging skin and the wound bed due to single or repeated removal of the silicone layer.
Despite the availability of a variety of absorbent wound dressings, there is a need and a demand for an improved wound dressing which prevents wound trauma upon wound dressing changes, improves the durability and lifetime of the wound dressing, anatomically conforms to a wound and possesses improved fluid uptake, retention and removal properties. Most importantly, it is desired to produce a wound dressing having an adhesive layer that does not possess the drawbacks of known adhesive layers, and instead, gently adheres and detaches from a wound site while providing superior fluid uptake. Moreover, there is a need and a demand for an improved method of forming such an improved wound dressing that is both simple and cost effective.